JPH0590697A - Manufacture of semiconductor laser - Google Patents

Abstract

PURPOSE:To improve the doping efficiency of a P-type dopant Zn, and to stand practical use even at a high growth temperature by bringing the growth rates of each semiconductor layer to a specific value or more. CONSTITUTION:The crystal growth rates of each semiconductor layer are brought to 2.5mum/h or larger. The graph gives the relationship graph of a crystal growth rate and carrier concentration. It shows results obtained in the case where a growth temperature of 720 deg.C and (dimethyl zinc)/(total amount of group III) = constant are used as growth conditions. Accordingly, the doping efficiency of a P-type dopant to a P-type (AlyGa1-1y)0.5In0.5P clad layer is improved by increasing the crystal growth rate, sufficient carrier concentration is obtained even at a high growth temperature ture aiming at the shortening of an oscillation wavelength, and the overall crystal growth time is shortened, and the diffusion of the dopant doped to the P-type clad layer to an active layer can also be reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser used as a light source for a laser printer, a bar code reader and the like, and more particularly to a method for manufacturing a visible light semiconductor laser having an oscillation wavelength of 680 nm or less.

[0002]

2. Description of the Related Art A conventional method of manufacturing a semiconductor laser will be described below. The structure of the semiconductor laser is shown in FIG. In the manufacturing method of the conventional example, the first crystal growth is performed at a growth temperature of 700 to 730 by a metal organic growth method (hereinafter, MO-VPE method).
At _0.5 ° C., a Ga _0.5 In _0.5 P active layer (4), which becomes a light emitting region, is formed on the n-type GaAs (100) substrate (1) with an (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P clad layer having a larger forbidden band. A double hetero structure composed of (3) and (5) is formed.

Next, an oxide film is formed which serves as an etching mask for forming a ridge stripe and a mask for selective growth.
An oxide film stripe is formed in the [0-11] direction by the photoresist method, and the p-type cladding layer (5) is formed by etching.
Etch halfway.

Subsequently, the crystal is grown for the second time, and selective growth is carried out using the oxide film as a mask to grow the current block layer (7). Then, after removing the oxide film, a p-type GaAs contact layer (8) is grown on the entire surface, electrodes (9) and (10) are attached, and a conventional semiconductor laser is obtained.

Among the characteristics of the semiconductor laser of the conventional example, the oscillation threshold greatly depends on the Zn carrier concentration of the p-type cladding layer (5). For example, the carrier concentration is 3.5 × 10 ^17.
The oscillation threshold is reported to be 38 mA at cm ^-3 . At this time, the resonator length is 300 μm. Further, the maximum oscillation density is 100 ° C., and the reliability is not reported. This conventional example is the 1989 Spring Biography Proceedings 8
See page 66, 1p-ZC-4.

[0006]

AlG according to the present invention
Ga _0.5 used for light emitting region of aInP-based semiconductor laser
For In _0.5 P, Japan Journal of Applied Physics (Jpn. J. Appl. Phy
s. ) 27, p2098 (1988), the band cap Eg changes with the crystal growth temperature Tg in the MO-VPE method.
If the growth temperature is raised, a semiconductor laser with a short oscillation wavelength can be obtained. However, it is generally difficult to dope Zn into the p-type cladding layer (5) when the growth temperature is increased. _{Further, (Al y Ga 1-y} ) 0.5 In 0.5 Zn doped with P is easily diffused, the temperature is high and the diffusion proceeds more, the reliability of the semiconductor laser is exacerbated especially Zn enters the active layer. Therefore, there is a problem that it is difficult to obtain a semiconductor laser having characteristics that can be used practically.

[0007]

According to the method of manufacturing a semiconductor laser of the present invention, the crystal growth rate of each semiconductor layer is 2.5 μm /
h or more.

[0008]

In the method of manufacturing a semiconductor laser according to the present invention, by increasing the crystal growth rate, p-type (Al _y Ga
_1-y ) _0.5 In _0.5 p The doping efficiency of the p-type dopant in the clad layer is increased, and a sufficient carrier concentration can be obtained even at a high growth temperature aimed at shortening the oscillation wavelength.
Further, all the crystal growth time is shortened, and the diffusion of the dopant doped in the p-type cladding layer into the active layer can be reduced.

[0009]

The present invention will be described below with reference to the drawings. FIG. 1 is a graph showing the relationship between the crystal growth rate and the carrier concentration, which represents the effect of the present invention. The growth conditions include a growth temperature of 7
The results are obtained at 20 ° C., [dimethyl zinc] / [total amount of Group 3] = constant. The reason why the carrier concentration is changed by increasing the crystal growth rate in this way is that the ratio of Zn atoms taken into the crystal and Zn atoms dissociated from the crystal into the vapor phase is changed. It is considered that the carrier concentration can be increased because the amount of Zn dissociated into is reduced.

FIG. 2 is a sectional view of a semiconductor laser manufactured at a crystal growth rate of 3.5 μm / h among the growth concentrations shown in FIG. First, the first crystal growth is performed by MO-VPE method at a growth temperature of 720 ° C. and a growth pressure of 30 Torr. The layer structure is as follows: Si-doped n-type GaAs buffer layer (2) Carrier concentration 1 × 10 ¹⁸ cm ⁻³ 0.2 μm on Si-doped GaAs (100) substrate (1)
_0.6 Ga _0.4 ) _0.5 In _0.5 P clad layer carrier concentration 5 × 10 ¹⁷ cm ⁻³ of 1 μm, undoped Ga _0.5 In
_0.5 P active layer (4) 0.07 μm, Zn-doped p-type (Al _0.6 Ga _0.4 ) _0.5 In _0.5 P clad layer (5), carrier concentration 5 × 10 ¹⁷ cm ⁻³ 1 μm, Zn
Doped p-type Ga _0.5 In _0.5 P layer (6) Carrier concentration 1
× 10 ¹⁸ cm ⁻³ is laminated in a thickness of 0.1 μm.

Then, a SiO ₂ oxide film is formed to a thickness of 0.2 μm to serve as an etching mask for forming the ridge stripe and a mask for selective growth.
1] direction, a SiO ₂ oxide film stripe is formed, and the p-type clad layer (5) is 0.25 μm with a sulfuric acid-based etching solution.
The remaining etching is performed. The ridge width W ₁ is 5 μm.

Next, the second crystal growth was performed by MO-VPE at a growth temperature of 650 ° C. on both sides of the ridge stripe.
Si-doped n-type GaAs current block layer (7) carrier concentration 3 × 1 by selective growth using O ₂ oxide film as a mask
0 ¹⁸ cm ⁻³ is grown to 0.8 μm. Then, after removing the SiO2 oxide film, the third crystal growth is performed by MO-VPE at a growth temperature of 650 DEG C. and Zn-doped p-type Ga is formed on the entire surface.
As contact layer (8) carrier concentration 2-10 ¹⁹ c
A semiconductor laser is obtained by growing m ⁻³ and a thickness of 3 μm and forming electrodes (9) and (10). The characteristics of the semiconductor laser are that the cavity length is 350 μm and the oscillation threshold is 35 to 30.
Characteristics up to mA, oscillation wavelength of 670 nm, and maximum oscillation temperature of 110 ° C. were obtained.

The semiconductor laser shown in FIG. 3 has the same growth conditions as in FIG.
After growing up to the current blocking layer (7), stripe-shaped grooves are formed in the [0-11] direction with a phosphoric acid-based etching solution by a photoresist method. Subsequently, the second crystal growth was performed by MO-VPE at a growth temperature of 650 ° C. on the entire surface with Zn.
Doped p-type GaAs contact layer (8) Carrier concentration 2
× 10 ¹⁹ cm ⁻³ , thickness 3 μm, electrode (9),
A semiconductor laser is obtained by forming (10). The characteristics of the semiconductor laser are that the resonator has an oscillation threshold of 75 mA at 300 μm, an oscillation wavelength of 670 nm, and a maximum oscillation temperature of 120 ° C.
The characteristics up to were obtained.

[0014]

As described above, according to the present invention, the crystal growth rate is set to 2.5 μm / n or more, as shown in FIG.
By improving the doping efficiency of the p-type dopant Zn, a semiconductor laser having laser characteristics that can withstand practical use even at a high growth temperature, for example, 720 ° C. can be obtained. The reason is that the time period during which the temperature is kept high during a plurality of crystal growths becomes short, so that Zn p that easily diffuses in the crystal is reduced.
Diffusion from the type cladding layer (5) to the active layer (4) can be reduced, a pn junction having a steeper than a conventional semiconductor laser can be obtained, and temperature characteristics are improved. For example, the semiconductor laser shown in FIG. 2 has a cavity length of 350 μm, an oscillation threshold of 40 mA, and an oscillation wavelength of 670 nm, and has a case temperature of 70 ° C. and an optical output of 5 mW. Has the effect of being obtained.

Further, since the growth time for one cycle is shortened, the productivity can be improved.

[Brief description of drawings]

FIG. 1 is a diagram showing a relationship between a crystal growth rate and a Zn carrier concentration according to the present invention.

FIG. 2 is a sectional view of a semiconductor laser manufactured according to the present invention.

FIG. 3 is a sectional view of a semiconductor laser manufactured according to the present invention.

FIG. 4 is a sectional view of a conventional semiconductor laser.

[Explanation of symbols]

1 n-type GaAs substrate 2 n-type GaAs buffer layer 3 n-type (Al _y Ga _1-y ) _0.5 In _0.5 P clad layer (0.5 ≦ y ≦ 1) 4 undoped (Al _z Ga _1-z ) _0.5 In _0.5 P active layer (0 ≦ z ≦ 0.3) 5 p -type _{(Al y Ga 1-y)} 0.5 In 0.5 P cladding layer (0.5 ≦ y ≦ 1) 6 p -type Ga _0.5 an In _0.5 P layer 7 n-type GaAs current blocking layer 8 p-type GaAs contact layer 9 and 10 electrodes

Claims (1)

[Claims] 1. A semiconductor substrate, at least n-type (Al _y G
a _1-y ) _0.5 In _0.5 P (0.5 ≦ y ≦ 1) cladding layer, (Al _z Ga _1-z ) _0.5 In _0.5 P (0 ≦ z ≦ 0.
3) an active layer, p-type _{(Al y Ga 1-y)} 0.5 In 0.5 P clad layer and a p-type Ga _0.5 In _0.5 P layer are sequentially grown by metal organic vapor phase growth method to form a multilayered structure,
Next, in a method of manufacturing a semiconductor laser in which a stripe structure is formed in a multilayer laminated structure, a growth rate of each of the semiconductor layers is set to 2.5 μm / h or more.